1. Field of the Invention
The present invention relates to a transmission device and, more particularly, to a transmission device having rolling contact surfaces for transmitting motion between first and second moveable elements.
2. Description of the Prior Art
The effective operation of any transmission device relies on an accurate meshing of the parts in contact. In gear trains, accurate meshing is relaxed in favor of assemblability, thereby giving rise to backlash and its well-known drawbacks. While backlash in gear trains intended for power transmission at a constant rpm can be tolerated, in automation, machinery, such as robots, the speed reverses its sign continuously and, in sensor-based systems, unpredictably. In automation machinery, therefore, backlash hampers seriously the machine performance.
Robotic applications have called for a revision of alternative transmissions. In this vein, it has been proposed to replace gear trains by transmission devices based on the pure rolling action of a cam with respect to a roller. The idea has been pursued in the past, as attested by the following patents:
U.S. Pat. No. 3,170,333 by Emil Umbricht discloses a rotary positioning device specifically aimed at the coupling of parallel shafts for the production of indexing motion. The device comprises a plurality of rollers meshing with conjugate cams. The patent discloses two conjugate cams of an asymmetric shape, with high curvature changes.
U.S. Pat. No. 3,525,268 by Ronald H. Kenny discloses a parallel shaft cam drive intended for the production of either indexing motion or speed reduction. As its name states, this device pertains only to the coupling of parallel shafts. It comprises also a plurality of rollers meshing with two conjugate cams which, as in the Umbricht patent, bear asymmetric shapes with high curvature changes.
U.S. Pat. No. 5,176,036 by William O. Harris discloses a parallel shaft drive and indexing machine which, as its name indicates, is limited to both parallel shafts and indexing motion. The morphology of the device is similar to those of the Umbricht and Kenny patents.
U.S. Pat. No. 5,247,847 by Inhoy Gu discloses a cam gear assembly that is intended as a speed-reducing device. The device consists of a periodically-convex plate, with a shape proper of gears, meshing with a plurality of rollers. The patent is mostly intended for the coupling of parallel shafts, but it also contemplates the coupling of intersecting shafts.
The patents recalled above comprise invariably a cam element with a shape exhibiting pronounced changes of curvature, which hampers (a) the accurate machining of the profile and (b) the strength of the cam.
It is therefore an aim of the present invention to provide a new transmission device which is adapted to produce uniform speed transmission between two moveable elements.
It is a further aim of the present invention to provide a transmission device which is adapted to transmit power from an input element to an output element through a transmission mechanism having rolling-contact, thereby generating low friction resistance and low power losses.
It is an aim of the present invention to provide such a transmission device comprising conjugate cams with fully convex cam profiles.
It is a further aim of the present invention to provide a transmission device which produces low backlash and which is thus particularly suitable in specific areas that call for high accuracy and smooth operations.
It is an aim of the present invention to provide a transmission device which operates at low noise level.
It is a further aim of the present invention to provide a transmission device which can be designed to couple parallel or intersecting shafts at angles varying from 0 to 180 degrees.
It is a still further aim of the present invention to provide a transmission device which is adapted to link a revolving shaft to a translating rack.
Therefore, in accordance with the present invention, there is provided a transmission mechanism for producing uniform speed transmission between first and second moveable elements, comprising a set of conjugate cams adapted to rotate with said first moveable element about a first axis, and corresponding arrays of spaced-apart rollers connected to said second moveable element for movement therewith, said set of conjugate cams being adapted to alternately cooperate with said spaced-apart rollers of said corresponding arrays of spaced-apart rollers to communicate continuous motion to one of said first and second moveable elements in response to a driving action of the other of said first and second moveable elements, wherein each said cam has a fully convex cam profile.